1. Field of the Invention
The present invention relates to a lift control device, and more particularly to a lift control device for a roller shade.
2. Description of Related Art
With reference to FIG. 6, a conventional lift control device for a roller shade comprises a support rod (80), a spring (82), a roller cap (86) and a follower spool (89). The support rod (80) is adapted to connect to a frame of the roller shade through a bracket (not shown). The spring (82) is mounted around the support rod (80) and has two coiled portions (83). Each coiled portion (83) has a bent distal end (85), and a connecting lug (84) is formed between the coiled portions (83). The roller cap (86) is rotatably mounted on the support rod (80) and has a retaining opening (87) corresponding to the spring (82). The bent distal ends (85) on the coiled portions (83) abut one side of the retaining opening (87), and the connecting lug (84) between the coiled portions (83) abuts the other side of the retaining opening (87). A chain retaining wheel (not numbered) is mounted on one end of the roller cap (86), and a loop-shaped chain (88) is secured to the chain retaining wheel to rotate the chain retaining wheel when the chain (88) is drawn. The follower spool (89) is attached on the roller cap (86) to rotate with the roller cap (86). The follower spool (89) is adapted to connect to a roller tube (not shown) on which a shade blind is mounted. An elongated rib (not numbered) is formed on the inner wall of the follower spool (89) and is located between the connecting lug (84) and the distal ends (85) of the coiled portions (83). When the chain (88) is drawn, the roller cap (86) will be rotated so as to push either the connecting lug (84) or the distal ends (85) of the coiled portions (83). The elongated rib will be pushed by the connecting lug (84) or the distal ends (85), such that the follower spool (89) will rotate with the roller cap (86). Accordingly, the lifting or lowering of the shade blind can be controlled by means of drawing the chain (88) through the lift control device.
However, the conventional lift control device has the following shortcomings.
1. Because there is a gap defined between the elongated rib and the connecting lug (84) or the distal ends (85) of the coiled portions (83), the follower spool (89) cannot be actuated in the instant when the chain (88) is pulled. The shade blind of the roller shade cannot be lifted or lowered a slight distance by the conventional lift control device.
2. The movement of the follower spool (89) is limited by the friction of the coiled portions of the spring (82) between the support rod (80). When a force applied to the shade blind is larger than the friction provided by the spring (82), the shade blind will be forced to lower. More specifically, a large shade blind having a weight larger than the friction provided by the spring (82) will unintentionally lower due to the weight of the shade blind. Thus the safety of using the conventional lift control device is not enough. The conventional lift control device cannot be used in a roller shade with a large shade blind, and the use of the conventional lift control device is not versatile.
3. The resiliency of the spring (82) will be lost after a long time of use, and the useful life of the conventional lift control device is inconveniently short.
To overcome the shortcomings, the present invention tends to provide a lift control device to mitigate or obviate the aforementioned problems.
The main objective of the invention is to provide a lift control device for a roller shade that can make a shade blind of the roller shade lift or lower instantly when a chain is drawn.
The secondary objective of the invention is to provide a lift control device for a roller shade to make the use of the lift control versatile and to improve the safety of use the shade blind.